It is known how to occlude an anatomic conduit by means of an occlusion system implantable into the body of a patient.
The occlusion of the anatomic conduit is ensured by an inflatable sleeve filled with fluid which exerts a more or less strong pressure on the portion to be occluded depending on the volume of the fluid in the inflatable sleeve.
For example, various urinary artificial sphincters are based on this principle for exerting pressure on the urethra. Among known products, mention may be made of the implant referenced as AMS800 marketed by American Medical Systems or else the implant referenced as ZSI375 marketed by Zephyr. The same principle is found in other types of applications such as gastric rings which include an inflatable sleeve placed around the stomach.
The swellable sleeve filled with fluid may be made in different forms, for example totally or partly surrounding the conduit to be occluded and may be formed with different biocompatible materials, such as implantable silicone, implantable polyurethane, etc.
The injection and the suction of fluid in the inflatable sleeve required for the occlusion of the anatomic portion may be either achieved manually and passively such as for artificial urinary sphincters AMS800 and ZSI375, or automatically and actively (from an electric power source for example) for more developed implants.
In order to allow regulation of the pressure exerted on the conduit to be occluded, the inflatable sleeve is in fluidic connection with a reservoir of fluid coupled with a configured actuator for injecting fluid from the reservoir to the sleeve (in order to increase the pressure exerted on the anatomic conduit) or from the sleeve to the reservoir (for reducing the pressure exerted on the anatomic conduit). The whole of the inflatable sleeve, of the reservoir and of the fluidic connection between them forms a fluidic circuit.
In such an occlusion system, it may be necessary to measure the pressure in the inflatable sleeve or in another point of the fluidic circuit, for example in order to check pressure when the actuator is disabled, or further for controlling the pressure generated by said actuator.
Document EP 1 584 303 thus discloses the use of a pressure sensor implanted on the occlusive sleeve. However such a solution cannot be achieved industrially since it poses problems of integration, bulkiness, seal and biocompatibility of the sensor.
For this purpose, there exist different types of pressure sensors.
Among the sensors which may be contemplated in an implantable system, pressure sensors based on a flexible membrane in contact with the fluid may be used. These sensors nevertheless have to be biocompatible, stable over time, and it is necessary to ensure a perfect seal of the sensor in order to avoid infiltration of fluid or of humidity into the sensor or the associated electronics.
A solution to this problem may be the use of a pressure sensor comprising a flexible metal membrane ensuring the seal of the system. However, such a sensor has several drawbacks. On the one hand, as the metal membrane of the sensor is thin, the manufacturing methods may be delicate. Indeed, the mechanical stresses due to thermal effects of the weld on the membrane may have an effect on the stiffness of the membrane which may induce significant disparities in the mechanical properties of the membrane. Moreover, this type of sensor is generally sealed and filled with a non-compressible fluid in contact with a pressure sensor strictly speaking. The method for assembling the different portions of the system (consisting of several tens of elements) is therefore delicate and costly. Finally, when the system is implanted, the fibrosis surrounding the different elements of the implant may induce a change in stiffness of the membrane and therefore a drift in the measurements over time.
Another problem to be solved is to be able to apply a defined and specific pressure on the anatomic conduit by consuming a minimum of energy.
A simple solution would be to use a system based on the measured occlusion pressure. Among the means for measuring the occlusion pressure, mention may be made of systems which directly measure the pressure in the fluidic circuit via a suitable sensor, or else which measure the pressure indirectly for example from the current consumed by the actuator as described in document U.S. Pat. No. 8,585,580.
However, it has been demonstrated by tests in vivo [1] that the pressure in the fluidic circuit strongly and permanently varies during the occlusion. In the case of a system based on a pressure regulation, this has the effect of quasi-permanently urging the actuator for stabilizing the pressure at a given set value, with the consequence of inducing excessive electric consumption of the system.
Other principles have been proposed, for example document U.S. Pat. No. 8,585,580 proposes a system which transfers a fluid to the inflatable sleeve until the measured pressure exceeds a defined threshold. This solution has the drawback of not being very accurate on the applied occlusion pressure. Indeed, during the occlusion phase, the pressure may strongly increase and then decrease due to the relaxation of the tissues and of the occlusion device. The fluid provided to the occlusion device in contact with the anatomic conduit to be occluded is therefore generally not sufficient for generating the desired pressure.
Moreover, the bulkiness of such a sensor also poses a problem, insofar that the implantable system has to be of dimensions as reduced as possible and that said system further comprises a fluid transfer device, the volume of which has to be consequent and a battery which also represents a large portion of the volume of the implantable system. The integration of such a sensor into this system may be difficult due to the bulkiness of said sensor. Further, as this type of sensor has to be both in contact with the outside, and for the pressure measurement, and with the inside for communicating with the electronic module, it is necessary to apply a reliable and hermetic manufacturing process, such as laser welding, which may be a constraint in a production phase.